The present disclosure relates to a hybrid supercapacitor characterized by the constituents of its electrolyte.
Hybrid supercapacitors (HSCs), for example lithium ion capacitors, are a new generation of supercapacitors which can provide more power than lithium ion batteries. Although lithium ion batteries have a high energy density of more than 100 Wh/kg, they are able to release this energy only slowly. Hybrid supercapacitors have a higher energy density than supercapacitors (EDLCs/SCs), which are able to provide a power release of more than 100 kW/kg but have only a low energy density. Hybrid supercapacitors can be charged, for example, by means of short high-energy pulses as occur in the braking energy recuperation of motor vehicles. The electrical energy recovered in this way can subsequently be used to accelerate the motor vehicle. This enables saving of fuel and the reduction of carbon dioxide emissions. Hybrid supercapacitors are also being considered for use as an energy source in power tools. Since hybrid supercapacitors are a new technology compared to conventional supercapacitors and lithium ion batteries, only a few products are commercially available to date. Usually, in fields of application that would be suitable for hybrid supercapacitors, oversized lithium ion batteries are used, which, because of their size, are capable of providing the power required for the application in question.
E. Iwama, P. L. Taberna, P. Azais, L. Brégeon, P. Simon, Journal of Power Sources, 2012, 219, 235 states that the electrolytes most commonly used in hybrid supercapacitors contain acetonitrile or propylene carbonate as solvent. The use of such hybrid supercapacitors is limited to temperatures of not more than 70° C. R. S. Borges, A. L. M. Reddy, M.-T. F. Rodrigues, H. Gullapalli, K. Balakrishnan, G. G. Silva, P. M. Ajayan, Nature 2013, 3, 2572 reports that the operating range of supercapacitors can be extended to up to 200° C. when electrolytes consisting of a mixture of an ionic liquid with clay are used. However, even higher temperatures are inaccessible for the operation of hybrid supercapacitors.
In addition, the operation of hybrid supercapacitors, in the case of use of acetonitrile and propylene carbonate as solvent of the electrolyte, is limited at the lower end to a temperature of −55° C. Low Temperature Supercapacitors, NASA Tech Briefs, July 2008, 11-12, describes the use of ethyl acetate and methyl formate as cosolvents of the electrolyte. Even through use of these cosolvents, however, it is only possible to lower the lower temperature limit down to −60° C.